Physiological responses and tolerance of kenaf (Hibiscus cannabinus L.) exposed to chromium

• Cr-toxicity decreased the plant growth of Hibiscus cannabinus L.
• Hibiscus cannabinus L. has a great accumulation capacity for chromium.
• Antioxidant enzymes and non-protein thiol pool contribute to chromium tolerance.
• Zhe50-3 was found to be more sensitive than K39-2 under Cr stress.
• Roots are the primary site of metal injury and accumulation.

Selection of kenaf species with chromium (Cr) tolerance and exploring the physiological mechanisms involved in Cr tolerance are crucial for application of these species to phyto-remediation. In the present study, a hydroponic experiment was conducted to investigate the variation in two kenaf cultivars, K39-2 and Zhe50-3 under Cr stress. At the same Cr concentration, the tolerance index (TI) of K39-2 was higher than that of Zhe50-3, indicating that K39-2 may be more tolerant to Cr than Zhe50-3. It was also observed that high concentration of chromium was accumulated both in the shoots and the roots of Hibiscus cannabinus L. The leaves of K39-2 accumulated 4760.28 mg kg−1 of dry weight under 1.50 mM Cr stress, and the roots accumulated 11,958.33 mg kg−1. Physiological response shows that the antioxidant enzymes’ superoxide dismutase (SOD), catalase activity (CAT) and peroxidase (POD) activities increased in the leaves and decreased in roots of the Cr-stressed plants nearly compared to the control. Moreover, the variation of antioxidant enzymes activities indicated Zhe50-3 was more vulnerable than K39-2, and the contents of the non-protein thiol pool (GSH, NPT and PCs) were higher in K39-2 than Zhe50-3 with the increased Cr concentration. Based on the observations above, it can be concluded that the well-coordinated physiological changes confer a greater Cr tolerance to K39-2 than Zhe50-3 under Cr exposure, and Hibiscus cannabinus L. has a great accumulation capacity for chromium.